1. Field of the Invention
This invention relates to a reflector using a light-reflecting film which is formed of a flexible substrate, such as a plastic film, as a base material and a thin metal film of high reflectance overlayed on the substrate.
The reflector according to this invention can be used as a reflecting plate for a mirror or the like or as a reflecting plate (lamp house) for a fluorescent lamp which is in turn employed as a backlight source of a liquid-crystal display panel adopted in a word processor, notebook computer or the like.
2. Description of the Related Art
Compared with mirrors using glass as a base material, light-reflecting films with a flexible substrate such as a plastic film or the like are lighter in weight and also better in impact strength and flexibility. By processing and/or working these light-reflecting films either as they are or after laminating them with an aluminum plate or the like, their utility is spreading as reflectors for copying machines, solar energy collectors, light reflectors for vegetable plants, high-performance light reflectors for fluorescent lamps, and reflectors for backlights in liquid-crystal displays.
Keeping step with the reduction in thickness and size of liquid-crystal displays in recent years, reflectors having a primary reflection area whose radius 3 of curvature is 10 mm or less as shown in FIG. 5 have begun to find increasing utility as reflectors (lamp houses) for backlights. Employed as such reflectors 1 include those obtained each by bending a reflector composed of a base 8 such as an aluminum plate and a coating film 4' of a resin or the like formed on the base as well as those obtained each by inserting a film with a high-reflectance metal layer such as a silver or aluminum layer thereon inside a base, such as an aluminum plate, bent in advance so that high reflectance can be achieved.
In addition to the above-described demand for the reduction in thickness and size of liquid-crystal displays, it is required especially recently to increase the light quantity of backlights in view of the adoption of color liquid-crystal displays.
The insertion of a film with a high-reflectance metal layer such as a silver or aluminum film inside a base, such as an aluminum plate, bent in advance involves problems in productivity and performance as a reflector such that the insertion is very cumbersome and irregular reflection may occur due to misalignment of the film so inserted or displacement of the film from a circle concentric with the outer circumference of a fluorescent lamp as a light source.
The present inventors studied the bending workability of reflectors, each formed by overlaying a film, which carried a high-reflectance metal layer formed thereon, on a base via an adhesive in a usual manner. As a result it was found that one having good performance as a reflector after bending could not be obtained unless its radius of curvature were substantially large, for example, 20 mm or greater. It was also found that--as the radius of curvature was progressively reduced, for example--wrinkles occurred in the film on the bent surface or blisters occurred between the film and the base such as an aluminum plate although the bending of the base was feasible. This was found to result in the problem that the reflecting ability of the reflector would be lowered or the reflecting surface of the reflector would become uneven, thereby failing to function as a reflector for a backlight.
To produce a reflector having a small radius of curvature, for example, of 5 mm or less, there has hence been no choice other than relying, despite its low productivity, upon a process wherein a plastic film carrying thereon a high-reflectance metal layer such as a silver or aluminum layer formed by evaporation or the like is wound directly on a fluorescent lamp or a film with a high-reflectance metal layer such as a silver or aluminum layer formed thereon is inserted, in a base, such as an aluminum plate, that has been bent in advance.
A reflector made of a general plastic film and a thin silver film layer formed thereon provides high reflectance at an initial stage of its use so that it can provide high luminance when employed as a reflector for a fluorescent lamp. When the present inventors evaluated it by continuously using the same as a reflector for a fluorescent lamp, a reduction in luminance was observed after the passage of several hundreds hours. It was found that its luminance would abruptly drop when continuously employed for a period as long as about 2,000 hours. In the course of an investigation for its cause by the present inventors, the reflector was found to involve the technological problem that its reflectance significantly drops by environmental factors such as heat and light, especially by ultraviolet rays from the fluorescent lamp and fails to function as a reflector for a fluorescent lamp as a backlight.